Hydraulic thermostat bulb shielding means



March 27, 1962 w. R. WEEKS HYDRAULIC THERMOSTAT BULB SHIELDING MEANS Filed Nov. 16, 1960 INVENTOR.

WALTER R. WEEKS H \S ATTORNEY United States Patent 3,027,444 HYDRAULIC THERMOSTAT BULB SHIELDING MEANS Walter R. Weeks, Windy Hills, Ky., assignor to General Electric Company, a corporation of New. York I Filed Nov. 16, 1960, Ser. No. 69,764

8 Claims. (Cl. 219-65) The present invention relates to cooking ovens for domestic use and particularly to a means of protecting a hydraulic thermostat bulb in a domestic oven which is designed to operate through two temperature ranges such as a normal cooking range having a maximum temperature of about 600 F. and a higher heat cleaning range having a maximum temperature between 750 F. and 950 F.

Hydraulic thermostats having an elongated bulb or probe formed on the end of a capillary tube that is joined to a bellows or diaphragm within the thermostat housing have been widely used as oven thermostats for many years. The normal oven cooking temperatures have all been below about 600 F. maximum, and a thermally responsive fluid used in the hydraulic control system have been able to withstand this degree of temperature without difiiculty. However, the known thermally responsive fluids that are commercially acceptable cannot be operated at temperatures much above this value.

This invention contemplates the provision of a protective arrangement for the thermally responsive fluid so that a thermostat of the hydraulic type may be used successfully as a control element in the high temperature oven described and claimed in the co-pending application of Bohdan Hurko, Serial No. 27,926, filed May 9, 1960, which is assigned to the General Electric Company, the same assignee as in the present invention. As there describedand claimed, the oven is provided with an automatic oven cleaning cycle where the temperature of the oven is raised to a heat cleaning temperature within a range of 750 F. and 950 F. so as to burn 01f all food soil and leave the inner walls of the oven cavity perfectly clean.

The principal object of the present invention is to pro vide an adjustable shielding means for the bulb of a hydraulic thermostat and an air cooling means for the bulb when it is so shielded so that the oven temperature may be raised to the vicinity of 950 F. without injuring the bulb or the fluid carried therein.

A further object of the present invention is to sea-1 the bulb of a hydraulic thermostat from the oven air while placing the bulb in a cool air stream when the oven is operating in its abnormal high temperature condition so as to hold the maximum temperature of the bulb below a safe operating limit.

A still further object of the present invention is to provide an adjustable shielding means for the bulb of a hydraulic thermostat so that the bulb is in a cool air stream when the oven temperature is to be raised to an abnormal high temperature, and means are provided for throttling the exhaust to a certain degree when the oven is operating during normal cooking and to another degree when the oven is operating at the abnormal high temperature.

The present invention is incorporated in an oven which has controlled heating means capable of elevating the oven temperature to a value materially in excess of 600 F. in accordance with the invention of the aforementioned co-pending application of Bohdan Hurko. For controlling the heating means, a hydraulic thermostat is provided having a bulb filled with a thermally responsive liquid and arranged to be placedin a heat sensitive position in the oven. An adjustable shielding means is combined with the thermostat bulb to seal the bulb from the oven air before the oven temperature is raised to an abnormal high temperature. In addition a cool air supply duct delivers cool air over the bulb when it is sealed by the shielding means so that the bulb temperature will always be below the oven air temperature andlikewise below the maximum safe operating temperature of the thermostat fluid. A separate cool air exhaust and a separate hot air exhaust is provided for separating the oven air from the cooling air. While a blower could be used for forcing cool air to the thermostat bulb I prefer to take advantage of convection currents obtained by a natural draft of air through the cool air supply duct for absorbing some of the heat of the bulb and successfully restricting the thermostat bulb temperature to a maximum temperature of about 600 F. while at the same time the oven temperature will rise to as high as 950 F. during the heat cleaning cycle.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appending claims.

FIGURE 1 is a fragmentary side elevational view partly in cross-section of a free-standing electric range showing the thermostat bulb shielding means embodying the present invention.

FIGURE 2 is a partial view similar to that of FIGURE 1 showing the shielding means over the thermostat bulb where the shielding means has been adjusted from the normal position during cooking of FIGURE 1 to a sealed position which isolates the bulb from the high temperature of the oven air and places the bulb in a cool air stream.

Referring in detail to the drawing and in particular to FIGURE 1, this invention has been shown in one form as app-lied to a free-standing electric range 10, but it should be understood that this is for illustrative purposes only and that the invention is broad enough to be used in all domestic ovens whether they be heated by gas or electricity. The range 10 includes a top cooking surface 11 having a plurality of metal-sheathed surface heating elements 12, a back'splasher 13 containing the various manually adjustable control devices 14 for both the surface heating elements and the oven elements, and an oven cavity 15 formed by an oven liner 16 and a front-opening that no further description will be given of the other features of the range which form no part of the present invention. 7 Y

The oven liner 16 is a box-like construction having a bottom wall (not shown), parallel side walls 18, a back wall 19, and a top wall 20 as well as an open front that is adapted to be closed by the front door 17. As in standard electric ovens there is a lower heating element or baking unit (not shown) and an upper heating element or broil unit (not shown) which is disposed slightly below the top wall 20 of the oven liner. Both the bake and broil units may be plug-in units that are inserted into electrical connectors or receptacles positioned in suitable openings in the back wall 19 of the oven liner. 'Ihe oven liner 16 is surrounded by a relatively thick blanket of insulation 21 formed of a suitable material such as fiberglass or the like for preventing the escape of heat from the oven cavity as well as to hold down the operating temperature of the outer surface of the range body 10'.

It has been found that the walls of the oven liner may be cleaned automatically without hand scrubbing if the 'oven wall temperature is raised to a temperature between about 750 F. and 950 F. and held for a suitable length of time for burning off the food soil and grease spatter.

Also it is known that if the temperature does not reach a sufiiciently high value in some particular area of the oven liner, the soil will not be completely removed from construction of the front portion of the oven will not be discussed here as they do not form part of the present invention.

During the heat cleaning cycle, smoke and odors are generated from the food soil and grease spatterings that are being burned oifthe surfaces of the oven liner. This smoke must be eliminated. otherwise it might become toxic and cause bodily harm. Accordingly. the gases and grease laden water vapor. created in the oven cavity are discharged through an. exhaust duct25 which empties into a-smoke eliminator such as; the catalyticsmoke eliminator .26 of the general type disclosed in. the United States patent to Stanley B. Welch, No. 2,900,483, entitled Electric. Catalytic Contact Device and dated August 18, 1959, which is assigned to the General Electric Company the sameassignee as in the present invention. The house ing of the smoke, eliminator is formed by a pair of pan- 1 shape members 27 and 28 which are fastened-together ;by rivets 29 alongthe outer periphery thereof. A partition. 30 divides the housing into two sections, a large section 31 and a smaller section 32. These two sections arejoined by a ring of openings 3-3 which are formed in the partition and extend completely around the housing. The larger section 31 of the housing incorporates a coiled metal sheathed heating unit 34 which is similar in basic extend for nearly the entire length of the housing. The openings 44 and 46 are generally opposite each other,

while the openings 45 and 48 form a pair that are likewise opposite each other. jacent the slot 46. 'The rotatable damper 43 is tubular in shape and has a generally D-shaped cross-section with a pair of opposite openings 50 and 51 in the rounded section of the tube for purposes which will be explained hereinafter.

A cool air supply duct 52 is verticallydisposed behind the back wall 19 of the oven liner and it has an inlet end (not shown) located near the base of the rangeltl 12 mentioned previously; A catalytic screen 35 is positioned in parallel relation to the coiled heating unit 34 so that the oven etfiuent must make multiple passes through the screen and over the several turns of the heating element before passing through the ring of openings 33 in the-partition 30. The heating element 34. is energized by means of suitable electrical connections (not shown) so as to heat the catalytic screen 35 to its optimum reaction temperature for oxidizing the. oven effluent and convertingthe smoke particles into less obnoxious gases such as carbon dioxide and water vapor. The top of the smoke eliminator 26 extends into a horizontally disposed air duct 37 under the cooking surface 11 that has a vertical extension 38 communicating with the underside of one of the surface heating elements 12 through which it discharges. It will be understood that the vertical extension 38 is horizontally ofifset from the smoke eliminator 26. so as to avoid the direct spillage of fluids into the smoke eliminator.

As shown in both FIGURES 1 and 2, there is a standardelongated thermostat bulb 40 that extends alongthe back wall 19 of the oven liner near the top thereof. One end of the bulb is closed while the other end is joined to a capillary tube (not shown) that connects to a bellows or diaphragm (not shown) with an oven thermostat 14 that is located in the backsplasher 13 of the range so that the temperature changes within the oven may be reflected by the expansion and contraction of the fluid contained within the bulb. It hasbeen found necessary to limit. the maximum temperature of the fluid within the bulb 40 to about 600 F. while the oven air temperature must reach as high as from 750 F. to 950 F.

My invention accomplishes this purpose by the use of an adjustable shieldingmeans 41 which encompasses the thermostat bulb 4G and includes both a. cylindrical housing 42 and a rotating. damper 43. The cylindrical housing 4?, isprovided with a series of five longitudinally exand an. outlet end 53 that is fastened over the slot 48 in the housing 42 of the shielding means. Similarly there is a cool air exhaust duct' 54 that has one end fastened over the slot 45 in the cylindrical housing while its 012- posite end extends outwardly andupwardly through a suitable opening in the top wall 2t? of the oven liner and dis charges under the cooktop 11 as at 55. Looking at FIG URE 1 it is seen. that the rotatable damper 43 is turned to one position where it covers over the opening 48 in the cool air supply duct 52 as well as the opening 45in the cool air exhaust duct 54. Moreover, the damper stops any air fiow through slot 47. The presence of cool air is shown by the elongated arrow lines 49. At the same time the opposite openings 50 and 51 of'the damper 43 are in alignment with the slots 44 and 46 to allow the oven exhaust to pass out through the smoke eliminator 26. This is theposition of the damper as shown in FIGURE 1 during the normal cooking operations where:

the thermostat bulb is exposed to the oven air temperatures and to the radiant energy from the oven heating elements previously mentioned. Accordingly the hot oven exhaust is as shown by the dotted arrow lines 60 indicating that the hot oven air flows over the bulb 40 through the exhaust duct 25, the smoke eliminatorzo, and out through the ducts 37 and 38, At the same time the relatively cool room air present in the air supply duct 52 is blocked by the damper 43 from flowing over the bulb.

Note that in FIGURE 2 the damper has been rotated clockwise about so as to close the slot 44 and open the slots 48, 45, and 47, while the slot 46 is always left open because it communicates with'the smoke eliminator 26 to facilitate the removal of the oven exhaust whenever a the heating means of the oven are energized. This is erated on an automatic heat cleaning cycle and the oven air is to rise to a temperature between about 750 F. and 950 F. In order. to insure that the maximum tern perature of the bulb 40 does not rise above 600 F. the bulb 40 is sealed from the oven air temperature by the 90 rotation of the damper, and the bulb isplaced in a cool air stream which flows through the air supply duct 52 by convection that is assisted by the warm temperature of the back wall 19 of the oven liner. It is important not to mix the relatively cool room air with the high temperature oven air and this is accomplished by the damper allowing the oven air to pass through the slot 47 in the cylindrical housing 42 and then through the slot 46 where it moves through the exhaust duct 25, the smoke eliminator 26, and then through the ducts 37 and 38. Moreover, the damper serves to throttle the oven exhaust in varying degrees during normal cooking as compared with the heat cleaning cycle to avoid the cooling down of the oven during heat cleaning.

Having described above my invention of a simple adjustable shielding means for a thermostat bulb in a high temperature oven, it will be readily apparent to those skilled in this art that this invention is not limited to the particular embodiment disclosed which show a long cy- Finally the last slot 47 is ad-.

to be noted that the cylindrical housing for the damper need not be located exactly as shown, but that it could be built into the back wall 19 of the oven liner completely out of the way of any cooking utensils that might be placed in the oven. Likewise the air supply duct 52 and the air exhaust duct 54 could both be located at the back of the oven liner in order to simplify the construction and remove as much structure as possible from the oven cavity.

Other modifications of this invention will occur to those skilled in this art and it is to be understood, therefore,

, that this invention is not limited to the particular embodiments disclosed but that it is intended to cover all modifications which are within the true spirit and scope of this invention as claimed.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A hydraulic thermostatic control system for controlling the heating means of an oven, said control system comprising a thermostat bulb fixedly mounted within an oven, a temperature responsive fluid filling said thermostat bulb for controlling said heating means responsively to the expansion and contraction of the fluid, and protective means for preventing an excessive temperature rise in said fluid, said protective means including an adjustable shielding means having one position for sealing the thermostat bulb from the oven air and a second position that exposes the bulb to the oven air, there being a supply duct directing cool air over the bulb when the shielding means is sealed over the bulb, and a first exhaust duct leading from the bulb for causing the cool air to flow past the bulb and through the exhaust duct, a second exhaust duct leading from the vicinity of the bulb for removing the hot exhaust gases from the oven when the bulb is sealed by the shielding means in its first position, the shielding means in its second position sealing otf both the cool air supply duct and the first exhaust duct while exposing the bulb to the oven air and opening the second exhaust duct to remove the oven air by passing the oven exhaust over the bulb and out the second exhaust duct.

2. A hydraulic thermostatic control system for controlling the heating means of an oven, said control system comprising a thermostat bulb fixedly mounted within an oven, a temperature responsive fluid filling said thermostat bulb for controlling said heating means responsively to the expansion and contraction of fluid, and protective means for preventing an excessive temperature rise in said fluid when the temperature within the oven rises to an amount above the safe operating temperature of the fluid in the bulb, said protective means including an adjustable shielding means in combination with a cool air supply duct so that when the oven temperature is to 7 rise to an excessive high temperature the shielding means seals the bulb from the oven air and connects the bulb to the flow of cool air from the air supply means so that the temperature of the bulb is kept below its maximum safe temperature while the oven temperature rises beyond this point, the adjustable shielding means being movable to a position for sealing the air supply duct and exposing the bulb to the oven air for normal cooking operations.

3. A hydraulic thermostatic control system as recited in claim 2 with the addition of a first exhaust duct directed toward the thermostat bulb for removing the cool air from around the thermostat bulb when the shielding means seals the bulb from the oven air, and a second exhaust duct for removing the oven air in both positions of the shielding means, both the air supply duct and the first exhaust duct being closed when the thermostat bulb is exposed to the oven air during normal cooking operations.

4. A hydraulic thermostatic control system as recited in claim 3 wherein the cool air supply duct extends down the back of the oven and has an inlet end that is open to room air, this relatively cool air being moved by convection through the duct and over the thermostat bulb, and a smoke eliminating device located within the second exhaust duct for removing large portions of the odor and smoke from the oven efiluent.

5. A domestic oven having a hydraulic thermostatic control system for controlling the oven heating means, the hydraulic thermostatic control including a bulb filled with a heat sensitive fluid, shielding means for protecting the thermostat bulb from rising above a maximum allowable temperature when the temperature of the oven air rises above said maximum allowable temperature, said shielding means including a damper which in one position exposes the bulb to the oven air temperature and in another position seals the bulb from the heat within the oven, and air circulation means cooperating with said shielding means for directing relatively cool air over the bulb while the bulb is sealed by the damper, said circulation means being rendered inoperative by the damper when the damper exposes the bulb to the oven air.

6, A domestic oven, heating means for the oven for normal cooking operations as well as for an automatic heat cleaning cycle to burn off the food soil of the inner walls of the oven, a hydraulic thermostatic control means for controlling the oven heating means and including a thermostat bulb mounted within the oven, a temperature responsive fluid filling said bulb, and shielding means cooperating with the thermostat bulb to limit the temperature of the bulb below a maximum allowable temperature while the temperature of the oven air rises above this maximum temperature during a heat cleaning cycle, said shielding means comprising a damper having at least two positions, a first position exposing the bulb to the oven air during normal cooking operations, and a second position overlying the bulb for sealing the bulb from the oven air, a cool air supply duct cooperating with the damper and being opened by the damper when the damper seals over the bulb so that the cool air absorbs heat from the bulb and carries the heat outside of the oven, said damper closing the air supply duct when the damper exposes the bulb to the oven air.

7. A domestic oven as recited in claim 6 wherein the air supply duct has a natural draft that is provided by the inlet end of the duct being positioned below the oven, and the central portion of the duct being located closely adjacent the back wall of the oven so that the heat from the oven is transmitted to the air in the duct to accelerate the air movement.

8. A domestic oven as recited in claim 6 wherein the oven has at least two exhaust ducts, a first exhaust duct that is always open to remove the exhaust from the oven during both normal cooking operations and the heat cleaning cycle, a second exhaust duct cooperating with the References Cited in the file of this patent UNITED STATES PATENTS 2,864,358 Harding Dec. :16, 1958 FOREIGN PATENTS 732,120 Great Britain June 22, 1955 

